Diesel engines typically employ replaceable cylinder liners made of various grades of cast iron, such as grey iron. Cast iron is selected, in part, because graphite at the interface between the liner and a piston ring acts as a lubricant and provides wear resistance. Heat treating the surface of cast iron alloys may also increase wear resistance by forming a hard, martensitic microstructure.
Further, engineers are designing thinner liners in an effort to increase the displacement of the cylinders to extract more power from the engine. However, thinned grey iron liners may not have sufficient strength properties, leading to flange fatigue and eventual structural failure of the liners. Accordingly, another material was examined for such thin liner applications.
One category of material that has been explored is steel alloys, since they provide improved strength and creep resistance. An exemplary application of steel liners is discussed by Azevedo et al. (U.S. Pat. App. Pub. 2005/0199196). However, Azevedo et al. note that steel liners are not suitable for use in heavy-duty wet lined engine applications, and propose to solve that issue. In dry lined applications, the surface of a steel liner must be hardened to nearly completely martensitic structure on the wear surface. But creating a specific microstructure in steel liners is highly dependent on the processing techniques, and primarily on the heat treatments employed. For example, the typical combination of a furnace cool from normalizing temperatures results in a lamellar structure and is, appropriately, called a lamellar anneal. The lamellar structure includes large grains of pearlite and ferrite, which form during the slow furnace cooling, and large regions or bands of ferrite. Subsequent induction hardening heat treatment(s) can quickly dissolve the pearlite, but large domains of ferrite may persist even after two induction hardening heat treatments because of insufficient time for ferrite dissolution. These large domains of ferrite artifacts may inhibit the performance of the steel liner by potentially promoting cyclic creep in the liner, resulting in ovalization and, eventually, seizure of the piston. Moreover, even without ovalization, the soft ferrite domains may lead to piston seizure because of their low scuffing resistance.
The present disclosure is directed to overcoming one or more of the problems as set forth above.